Cushioning devices are used to protect railcars and lading from impacts during coupling and train action events. To absorb the high forces caused by these impacts, cushioning devices are employed between the frame of the railcar and couplers.
Impacts applied to railcars result in high forces applied to the coupler in both the buff direction and the draft direction. "Buff" is a term in the rail industry used to describe the movement experienced by the coupler when it is moved towards its associated railcar. "Draft" is a term in the rail industry used to describe the movement experienced by the coupler when it is moved away from its associated railcar. A buff impact moves the coupler towards its associated railcar. A draft impact moves the coupler away from its associated railcar.
Conventionally railcar impacts are cushioned by hydraulic cylinders. In one type of hydraulic cylinder, pressurized gas in hydraulic fluid in the cylinder biases the piston to a fully extended position. If a draft impact occurs while the piston is fully extended, the device is unable to cushion the impact because the piston cannot move further in draft. In another type of gas charged hydraulic cushioning device, an externally mounted spring prevents the pressurized hydraulic fluid from fully extending the piston and holds the piston in a neutral position. The piston can move from the neutral position in response to either buff or draft impacts. The external spring increases the size of the cushioning device and makes installation difficult. The external spring is exposed to dirt and other environmental contaminants that can adversely affect operation of the cushioning device. The restoring force generated by the external spring acts along a line of force eccentric with the line of action of the cylinder itself, and may cause uneven or accelerated wear of moving components.
Thus, there is a need for an improved gas charged hydraulic railcar cushioning device that can cushion both buff impacts and draft impacts without an external spring device, and has forces applied along the line of action of the cushioning device itself.